1. Field of the Invention
The present invention pertains to the field of liquid purification or separation, more specifically the separation of suspended solids from a liquid. The method and apparatus of the invention comprise the direct application of the suspension to the filter medium. The filter medium is moving, as the filter medium is in the form of a rotating drum. More specifically, the invention is concerned with an improved rotary drum vacuum filter, wherein the improved filter enables a high degree of particulate rising of easily eroded particulates, such as small catalyst particulates having a relatively high surface area per unit weight, or other finely divided particles.
2. Description of the Prior Art
Applicant is aware of the existence of many prior art U.S. patents relating to rotary drum vacuum filters. However, applicant believes that U.S. Pat. No. 4,008,154 is closer to the present invention than any other prior art of which applicant is aware. Accordingly, the relationship of the present invention to U.S. Pat. No. 4,008,154 is discussed immediately below in detail. Other more distantly related prior art includes the following U.S. Pat. Nos.: 3,729,414; 3,215,277; 2,698,687; 2,092,111; and 1,475,244. Applicant does not believe that any of these other prior art patents are close enough to the instant invention to be worthy of any detailed discussion.
U.S. Pat. No. 4,008,154 discloses a process and apparatus for rinsing a cake formed on a rotary drum vacuum filter. The apparatus has:
". . . at least one elongated hollow distributor pipe mounted radially outward of and above said drum . . . said pipe having a multiplicity of uniformly spaced axially aligned holes . . . disposed on said pipe . . ." (claim 1) PA1 "Wash liquid passes into the main distributor pipe 15 under pressure and then jets out at relatively high velocity through the . . . holes 15a . . . In a typical . . . application these holes . . . are . . . directed away from the filter cake." (column 4 11. 27-38) PA1 "Such filters can also be provided with spray nozzles mounted on distributor pipes. Since spray nozzles create relatively high velocity sprays, reasonably even distribution of liquid is possible at the outlet of the spray nozzles. However, the high velocities with which the spray issues have detrimental effects on the cake porosity and are undesirable. At the same time wash rates can vary widely depending on the nature of the wax crystals. When this occurs, the shape of the spray will change with the liquid pressure and coverage by the spray nozzles will be dependent upon the wash rate. Accordingly, at low wash rates poor coverage of the cake and poor washing often occurs." (Col. 2 11. 22-34)
In contrast, the instant invention utilizes no such distributor pipe. Furthermore, the '154 patent teaches that the:
In contrast, the instant invention utilizes sprayers for rinsing the filter cake, the sprayers being directed towards the cake. However, the '154 patent even teaches away from the use of sprayers in the filtration device:
Instead of impinging spray directly on the cake, the '154 patent drips the rinsing fluid down onto the filter cake, the rinsing fluid initially running off of the redistribution wire 18 as a small continuous stream, the stream breaking up into droplets before reaching the filter cake which is ordinarily about 4-8 inches below (col. 5 11 28-35 of the '154 patent). In contrast, the instant invention blocks at least part of the spray with a spray blocking means, the blocking means being positioned above the cake surface, the blocking means being separated from the cake surface by a maximum of two inches.
The '154 patent requires a "diffusion channel" and a "redistributing overwrap means". The instant invention utilizes no similar elements.